Breath Hold

Although swimming is a fun activity for people, we’re not very good at it compared to marine mammals. Fortunately for us, we don’t rely on having to swim, dive, or hold our breath in order to find food, the way a Weddell seal does. Our bodies and Weddell seal bodies are different physiologically. For example, even though we both breathe oxygen in order to stay alive, Weddell seal bodies differ from human bodies in that they are able to hold much more oxygen in their blood and their muscles than human bodies rather like an internal SCUBA tank. This allows the seals to hold their breath for much longer than we can. Since oxygen is necessary for muscles to be able to work, Weddell seals also have developed special ways of swimming that minimize the amount of oxygen their muscles use while they are diving, allowing them to conserve their internal SCUBA tank and stay underwater even longer. By compressing and moving the air in their lungs they can change buoyancy during the dive. These changes help them sink to the bottom of the ocean during the descent part of their dive and then surface like a balloon on the ascent portion. In this way they can take fewer flipper strokes – which enables the diving seal to save oxygen. Weddell seals can cruise around underwater with very little flipper movement at all, which lets them dive down hundreds of feet into the water and stay down for as long as over an hour! To watch a computer-animated Weddell seal dive, click here.

A Weddell seal dive pattern compared to the height of the Empire State Building.

Two Weddell seals interacting beneath a hole in the ice.

A Weddell seal dive pattern, with varying speeds indicated by colors on the left,
and flipper strokes per second indicated by colors on the right.

If this doesn’t seem remarkable to you, let’s do an activity to demonstrate how well-adapted Weddell seals are for diving, and why it’s a good thing that humans have grocery stores and refrigerators. Would we be able to survive if we had to find food the way a Weddell seal does? This activity should take approximately 1.5 hours to complete.

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